In general, the durability of a tire is determined by the durability of a belt and the durability of a bead. Much research for preventing separation of a bead portion of a tire has been conducted.
FIG. 1 is a sectional view illustrating a conventional bead portion 10 of a tire for preventing separation of the bead portion. As shown in the drawing, a carcass 12, which forms the basic frame of a tire, is arranged in the radial direction around a bead bundle 11, which is embodied as a high-strength steel wire. If a tire rolls in an overloaded or high-temperature state for a long time, high shearing stress is applied to a turnup edge portion 12a of the carcass 12 due to repeated compression and extension, which results in separation of the bead portion.
A typical reinforcement structure for preventing this problem functions to protect the carcass 12 using a steel chafer 14, which is embodied as a steel cord, and, if necessary, further using a nylon chafer 15. Further, in the conventional structure, in which the carcass 12 is disposed around the bead core 11, an empty space is filled with rubber, which is referred to as a bead filler 13. In the case of a large tire, in order to meet requirements thereof, a bead filler 13 is designed as two rubber members having different properties from each other. The rubber member located at a high position is referred to as an upper bead filler 13a, and the rubber member located at a low position is referred to as a lower bead filler 13b. 
Conventional structures of a bead portion of a tire are disclosed in Korean Patent Publication No. 2012-0067138, Korean Patent Publication No. 2013-0014878, and Korean Patent Publication No. 2013-0075792.
A tubeless tire is constructed such that an airtight rubber layer, which is formed of a butyl-based rubber, is directly adhered to the interior surface of the tire instead of a tube. Such a tubeless tire has an advantage in that air leakage is prevented, heat generation is low because there is no friction between a tube and a tire, the weight is reduced, and the assembly process is simple.
However, in the state in which a high pressure is applied to the tubeless tire, if heat is transferred to a rim flange portion from a brake drum or other components, the portion of the rubber that is in contact with the rim flange portion may be damaged. In order to prevent this problem, a conventional tire is manufactured such that the amount of rubber is increased so as to reduce the stress applied to the portion of the tire that is in contact with the rim flange portion. However, this manufacturing method is not so effective when cracks are formed in the steel chafer and the nylon chafer. Further, when cracks are formed in the edge portion of the carcass, the cracks spread along the interface of the steel chafer, and consequently a portion of the rubber that is in contact with the rim flange portion is easily cracked.